Origins: Malaysia Airlines Flight 370 disappeared over the South China Sea on 8 March 2014 with 239 persons(227 passengers and 12 crew members) aboard. On 14 March 2014, an article began circulating on the Internet positing that the U.S. Navy had diverted the missing airliner to a secret Navy base and captured it:

A new report circulating in the Kremlin today prepared by the Main Intelligence Directorate of the General Staff of the Armed Forces (GRU) states that Aerospace Defence Forces (VKO) experts remain "puzzled" as to why the United States Navy "captured and then diverted" a Malaysia Airlines civilian aircraft from its intended flight-path to their vast and highly-secretive Indian Ocean base located on the Diego Garcia atoll.

According to this report, Malaysia Airlines Flight 370 (also marketed as China Southern Airlines flight 748 through a codeshare) was a scheduled passenger flight from Kuala Lumpur, Malaysia, to Beijing, China, when on 8 March this Boeing 777-200ER aircraft "disappeared" in flight with 227 passengers on board from 15 countries, most of whom were Chinese, and 12 crew members.

Interesting to note, this report says, was that Flight 370 was already under GRU "surveillance" after it received a "highly suspicious" cargo load that had been traced to the Indian Ocean nation Republic of Seychelles, and where it had previously been aboard the US-flagged container ship MV Maersk Alabama.

This item was just more fictional "Sorcha Faal" sensationalism originating with a single disreputable source, the whatdoesitmean.com political conspiracy site, of which RationalWiki says:

Sorcha Faal is the alleged author of an ongoing series of "reports" published at WhatDoesItMean.com, whose work is of such quality that even other conspiracy nutters don't think much of it.

Each report resembles a news story in its style but usually includes a sensational headline barely related to reality and quotes authoritative high-level Russian sources (such as the Russian Federal Security Service) to support its most outrageous claims. Except for the stuff attributed to unverifiable sources, the reports don't contain much original material. They are usually based on various news items from the mainstream media and/or whatever the clogosphere is currently hyperventilating about, with each item shoehorned into the conspiracy narrative the report is trying to establish.